1. Field of the Invention
The present invention relates to a projection screen which displays images by receiving lights from a light source and its manufacturing method, and more particularly to a reflection type projection screen and its manufacturing method.
2. Description of the Related Art
Recently, overhead projectors and slide projectors are widely used as means for presenters to present materials in meetings and the like. In general households, video projectors and moving image film projectors are getting popular. In these projector units, lights outputted from a light source are spatially modulated to image lights by a light valve, and these image lights are projected on a projection screen through an illumination optical system such as a lens.
Some of this kind of projector units can display color images. In this case, a lamp, emitting white lights which contain three primary colors: red (R), green (G), and blue (B) is used as a light source, and a transmissive liquid crystal panel is used as a light valve. In this projector unit, the white light emitted from the light source is divided into a red ray, a green ray, and a blue ray by a illumination optical system, and these rays are converged on each given light path. These beams of light are spatially modulated by the liquid crystal panel corresponding to image signals. The modulated beams of light are combined as color image lights by a light composite part, and the combined color image lights are extended and projected on a projection screen by a projection lens.
Additionally, lately, as a projector unit which allows for displaying color images, a unit, using a narrow-spectrum three primary colors light source, e.g., a laser oscillator emitting respective narrow-spectrum lights for three primary colors as a light source, and using a grating light valve (GLV) as a light valve, has been developed. In this projector unit, each beam of light for each color emitted from the laser oscillator is spatially modulated by the GLV corresponding to image signals. The beams of light modulated in this way are combined as color image lights by a light composite part as in the projector unit. These combined color image lights are extended and projected on a projection screen by a projection lens.
Projection screens used for projector units are fell into two types: a transmission type wherein projection lights are illuminated from the rear side of the projection screen and seen at the front side; and a reflection type wherein projection lights are illuminated from the front side of the projection screen, and the reflected lights are seen at the front side. In either type, obtaining bright and high-contrast images are desired in order to realize a screen with good visibility. Further, in order to improve the storage efficiency, a projection screen, using polymeric materials as materials for a substrate and utilizing the flexibility of these polymeric materials is desired.
However, a projection screen, allowing for obtaining bright and high-contrast images and having the flexibility has not been realized. For example, in a projection screen 1000 shown in FIG. 1, the surface shape of the screen is devised by forming convex parts 1112A on the surface of a transparent layer 1112, and forming opaque layers 1113, made of blacking on the side surface of these convex parts 1112A, so that the black level is lowered and the brightness and the contrast are raised (for example, Japanese Patent No. 2889153) However, in this case, there are problems that its manufacturing cost is higher as lots of time and labor are taken with e.g. a process to form the convex parts 1112A and a process to form the opaque layers 1113, and the flexibility cannot be obtained.
Further, a projection screen 2000 shown in FIG. 2 comprises a substrate 1211. On the substrate 1211, a reflection layer 1212, a light absorption layer 1213, and a diffusion layer 1214 are sequentially formed (for example, Japanese Patent No. 3103802). The projection screen 2000 having such constitution has the flexibility as a whole, since its all layers are flexible. However, there are problems that as the position of the light absorption layer 1213 is closer to the light-entrance face side than the position of the reflection layer 1212 is, and almost all incidence lights are absorbed into the light absorption layer 1213, the white level is lowered, resulting in inability to obtain sufficient brightness and contrast.
Further, in the projection screen 2000, in the case where a light enters the screen face from the oblique direction, the light enters in a direction obliquely into the face of the reflection layer 1212, resulting in the change of the reflection characteristics and the occurrence of the color shift. Therefore, the color contrast is lowered and vivid images cannot be obtained. In particular, when the screen face is larger, such problem appears significantly.